The present invention relates to filtering separators, in particular pocket or tube filters, for cleaning smoke or dust-laden gases containing very fine, extremely adherent dust particles.
Certain dust particles, mostly those produced by sublimation and in particular those in smoke-laden gases from certain smelting plants, are very fine and as a result of this it becomes very difficult to separate them out in filtering separators such as pocket or tube filters. This is due to the fact that since the particles have a large surface area in comparison with their small mass they have a particularly pronounced capacity for adhesion and if they collide with some solid object they stick firmly to it and build up on it. Because of the strong forces of adhesion, the result of this build up of dust particles on one another and above all on the filaments of filter pockets or filter tubes is that the dust particles cannot be removed from the filter surfaces to an adequate degree, or in other words can only be partly removed, by known regeneration processes such as counter-current scavenging and/or joggling the filter tubes. This necessarily increases the resistance to flow through the filter, even when the filtering speed is low, to such an extent that the filtering system would in many cases need to be expanded to an economically unreasonable size.
To avoid the retention which occurs on the filter surfaces because of the strong adhesive power of the very fine dust, a prior proposal as disclosed in German patent specification no. 2,113,062; was to make it possible for the filter surfaces to be cleaned by countercurrent scavenging and/or joggling thereof accompanied by repeatedly feeding the dust which is thereby released from the filter surfaces as they are thus periodically cleaned, back to the filter surfaces as an entrainment in the dust-laden gas, so that there is agglomeration of the dust particles while in the suspended (extrained) state immediately before they reach the actual filter surfaces. The layer of dust on the filter surfaces thus remains permeable to gas, as a result of which the resistance of the filter to flow is prevented from becoming too great. This method has proved satisfactory so long as the adhesive power of the very fine dust does not exceed a certain level. If its adhesive power becomes too great, the dust particles which build up on one another and on and in the filter surfaces defy conventional cleaning methods and cling where they are, often remaining hanging in small clumps on the individual filaments. Even if there is provision for the feed-back of dust, this may then result in an irreversible clogging of the filter accompanied by a corresponding reduction in filtering speed and a sharp rise in resistance to flow through the filter.
It is an object of the invention to enable filtering separators, such as pocket or tube filters, in which the periodic cleaning of the filter surfaces is by countercurrent scavenging and/or joggling, to be used even when dust-laden or smoke-laden gases containing extremely adherent very fine dust are to be cleaned.